My system should have very little ventilation problems. My case is certainly big enough (Lian-Li PC-75), and there are two fans near it blowing outward.
I also had a PCI card in the slot two below it, but since I don't need it at the moment, I took it out. Now I have about 6 inches of space below the card, and plenty of space around it given the great size of the case (it's enormous).
This is just frustrating. I put my girlfriend's computer together last night, and it's basically the same system, but a Shuttle with onboard video. It had absolutely no problems playing the game at 800x600 (I didn't try higher - not enough time). My hardware can play the game at very high resolutions perfectly smoothly, but it only gives me about 4 minutes of playing, particularly if there's a lot of action. No slow down, just crashes.
Someone said it might be the chipset. Any advice on cooling that? I can't go through another motherboard exchange, particularly when that might not be the culprit.
Maybe I should get a Shuttle...
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Matt